The CEO of dairy giant Fonterra has described reaction to trace findings of nitrate inhibitor in milk as "way out of proportion".

Co-op chief Theo Spierings said he could assure consumers worldwide that Fonterra products were safe to consume.

"We know some of our customers and regulators have questions. We need to answer them, and that's exactly what we are doing," he said.

"We have strong science and we are providing assurances about the safety of our products. Our testing has found only minute traces of DCD in samples of some of our products. It is important to remember that the minute traces detected were around 100 times lower than acceptable levels under European food safety limits. "

On Friday Fonterra issued a press release saying it supported moves by New Zealand's two main fertiliser suppliers to voluntarily suspend sales and use of Dicyandiamide (DCD) treatment on farm land until further notice.

DCD is used to inhibit nitrate leaching into waterways from fertiliser treatments and to reduce greenhouse gas emissions.

The decision followed a finding in September that traces of DCD had appeared in milk tested by Fonterra. Spierings said talks with fertiliser companies Ravensdown and Ballnce agri-nutrients about withdrawing DCD from the market had begun at that time.

Todd Muller, managing director of co-operative affairs at Fonterra, said the problem with DCD use was that although Europe had standards for DCD traces, most countries didn't, which meant the issue could create barriers to Fonterra's exports.

"Because farmers were looking to DCD as a tool to mitigate farm environmental impacts," he said, "we could see a potential problem in future."

The press conference followed media headlines in the United States and China drawing attention to the DCD finding and questioning the safety of New Zealand milk.

Spierings said his concern was not about milk safety but about consumers being concerned by rumours rather than facts. "The whole industry is affected, based on rumours," he said.

The potential impact was enough to make sure the government was kept full informed, said Spierings.

"We have a 100 per cent open line [to the government] every day, because it's a New Zealand issue," he said.